Ion implanters are widely used in electronic device fabrication, including semiconductor manufacturing to control device properties. In a typical ion implanter, ions generated from an ion source are directed as an ion beam through a series of beam-line components that may include an analyzing magnet and a plurality of electrodes that provide electric fields to tailor the ion beam properties. The analyzing magnet selects desired ion species, and filters out contaminant species and ions having undesirable energies. Suitably shaped electrodes may modify the energy and the shape of an ion beam.
For high-energy ion implantation, typically 100 keV or greater, tandem acceleration is often used to accelerate ions to a desired high energy. A tandem accelerator may be disposed along the beam line of an ion implanter in order to generate sufficiently high energy to implant ions into a substrate at desired depths. In a tandem acceleration process, an electrostatic accelerator accelerates negative ions generated in a special ion source from ground potential up to a positive high-voltage terminal. The electrons on the negative ions are then stripped by passage through a charge exchange region (referred to as a “stripper”). The resulting positive ions are again accelerated as they pass to ground potential from the high negative potential. The ions emerge from the tandem accelerator with twice the energy of the high positive voltage applied to the tandem accelerator.
One problem with producing high-energy ion beams using a tandem accelerator is energy contamination may result from the stripping process. This energy contamination may reduce the yield of manufactured devices. More specifically, energy contamination may reduce the overall energy of the ion beam. As such, the depth with which the ions are implanted may be less than desired or may be unpredictable due to the energy contamination. This is particularly important as the complexity of the devices manufactured using ion implantation grows and as the physical size of the devices manufactured shrinks. As will be appreciated, as the device complexity grows and the physical size shrinks, the manufacturing process is more sensitive to energy contamination, which has a strong correlation to device yield. It is with respect to these and other considerations that the present improvements have been needed.